Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A typical cellular wireless communication network provides a number of base stations throughout a region, with each base station radiating to define one or more cellular coverage areas such as cells and cell sectors. The base stations may then be coupled to various network infrastructure that operates to control base station operation and to provide connectivity with one or more transport networks such as the public switched telephone network (PSTN) or the Internet. With this arrangement, a mobile station (such as a cell phone or other wirelessly equipped device) positioned in any coverage area of the network may be served by the base station and in turn may engage in communication with other mobile stations or with various entities on the transport network(s).
In each coverage area of the network, the serving base station may broadcast a pilot signal, reference signal, or the like that may help to identify the coverage area and distinguish the coverage areas from others in the vicinity, and that mobile stations may monitor as a basis to detect and evaluate coverage. In practice, a mobile station may monitor these signals in an effort to detect the best available coverage and may choose to register with the system and operate in the best coverage area that it detects. Further, the mobile station may then continue to monitor these signals to determine when it would be appropriate to hand off from one coverage area to another, and the mobile station may then engage in signaling with the network to facilitate that handoff.
When operating in a coverage area, a mobile station may be in an idle mode or an active/connected mode. In the idle mode, the mobile station is not engaged in a call (e.g., voice call or data session) but may generally monitor overhead signaling from the serving base station in an effort to detect any page messages or other information of interest. In the active/connected mode, on the other hand, the mobile station has an assigned radio connection with the base station and may engage in a call via that radio connection. In both of these modes, the mobile station may also continue to monitor signals in its serving coverage area and in other coverage areas in an effort to identify the best coverage, and upon detecting sufficiently better coverage may work with the network to facilitate handoff.
Certain wireless systems also enable a mobile station to be served by multiple coverage areas at once. In such a system, the mobile station may have an “active set” of coverage areas in which the mobile station is active/connected, and the mobile station may communicate the same data simultaneously in all coverage areas of the active set. Advantageously with such an arrangement, the mobile station can engage in a “soft handoff” process, through which a sufficiently stronger coverage area is added to the active set in place of a weakest coverage area while the mobile station continues to communicate seamlessly on one or more other coverage areas of the active set.
When a mobile station is engaged in a call in the active/connected mode, if the mobile station loses communication with the network, the mobile station may experience a dropped call. This may happen if the mobile station is active/connected in a single coverage area and loses communication with the base station serving that coverage area, or if the mobile station is active/connected in multiple coverage areas at once and loses communication with the one or more base stations serving those coverage areas. In practice, when a mobile station experiences a dropped call, the mobile station may responsively scan for coverage once again and then transition to idle in a best available coverage area.